sql - Left Join、Order by、MySQL优化

Question

我有这样的查询:

   SELECT m...., a...., r....
     FROM 0_member AS m                 
LEFT JOIN 0_area AS a ON a.user_id = (SELECT user_id 
                                        FROM `0_area` 
                                       WHERE user_id = m.id 
                                    ORDER BY sec_id ASC LIMIT 1)
LEFT JOIN 0_rank as r ON a.rank_id = r.id 
    WHERE m.login_userid = '$username'

想法是从 0_area 表中获取第一行，因此尝试进行内部连接。但是，它没有按预期工作。

在 0_area 和 0_member 之间，0_member.id = 0_area.user_id。但是，有多行 0_area.user_id，我想要具有最低 sec_id 值的行。

有什么帮助吗？

Answer 1

   SELECT m...., a...., r....
     FROM 0_member AS m               
LEFT JOIN (SELECT user_id, min(sec_id) minsec
           FROM `0_area`
           GROUP BY user_id) g1 on g1.user_id=m.id
LEFT JOIN 0_area AS a ON a.user_id = g1.user_id and a.sec_id=minsec
LEFT JOIN 0_rank as r ON a.rank_id = r.id 
    WHERE m.login_userid = '$username'